This invention belongs to the field of agricultural chemistry and provides to the art a method for controlling aquatic weeds.
Aquatic weeds often have detrimental effects on the environment or the economics of waters and wetlands, for example in wet areas such as parts of Florida.
Aquatic weeds for example clog waterways, plug up water-handling equipment or endanger the ecological balance. Inter alia, they affect fishing, navigation, transport, drinking water quality, swimming and watersports. The economic impact for control and management in general and in particular in recreational areas is estimated to be in the millions of dollars. Therefore, the development of herbicides effective against aquatic weeds is important.
A typical representative for inventively controlled aquatic weeds is hydrilla, which is known as a submersed, very prolific, mat forming species, possibly dominating the aquatic system that it is present in. High densities of hydrilla interfere with various water uses as outlined above. A typical representative is Hydrilla verticillata. 
The control of certain aquatic weeds is discussed in the following art.
Generally, aquatic weeds and herbicidal or biological methods for controlling them are known, for example from L. W. J. Anderson, Pest Manag. Sci., 2003, 59, 801-813 or Netherland M. D., Getsinger K. D. and Stubbs D. R., Outlooks Pest Man., 2005, 16(3), 100-105 or J. E. Gallagher and W. T. Hailer, Rev. Weed Sci., 1990, 5, 115-192.
One of the major herbicides used for controlling aquatic weeds such as Hydrilla verticillata is fluridone (1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone).
However, it became apparent that a number of new biotypes of hydrilla have developed increased tolerance or even resistance to fluridone. Therefore, there is a continuous demand to further develop efficient herbicides for controlling aquatic weeds in general. Above all, the need for a herbicide to control hydrilla species, in particular Hydrilla verticillata, specifically their biotypes being tolerant or resistant to the herbicide fluridone, is warranted.
p-Hydroxyphenylpyruvate dioxygenase (HPPD) is a relatively new target for bleaching herbicides. Inhibition results in the depletion of the plant plastoquinone and vitamin E pools, leading to bleaching symptoms. These herbicides are very potent for the selective control of a wide range of broadleaf and grass weeds in maize and rice (see for example M. Matringe et al., Pest Manag. Sci., 2005, 61, 269-276).